In a chain saw used for cutting trees or the like, a saw chain wrapped around a circumferential portion of a guide bar that extends forward from a main body is driven by a power source such as an engine or a motor provided in the main body. In this case, the saw chain is driven when a driving gear around which the saw chain is wrapped is rotationally driven, a side wrapped around the driving gear in the saw chain serves as a chain meshed with the driving gear, and a side opposite to the side wrapped around the driving gear and the guide bar serves as a cutting tool. Thus, a cutting operation can be performed by the saw chain that runs along the circumferential portion of the guide bar at a high speed. A structure of such a chain saw is described in Patent Literature 1. When the engine is used as a power source, a rotation shaft (driving shaft) of the driving gear and a crankshaft (power shaft) of the engine are connected via a centrifugal clutch. In an idling state in which a rotational speed of the crankshaft is kept low, the centrifugal clutch is not connected, and the driving gear and the saw chain are not driven.
An operator grips a rear handle provided at a rear part of the main body and a front handle which protrudes upward from a front part of the main body and is provided at a rear part of the guide bar, brings the vicinity of a front end of the guide bar into contact with trees or the like and thus can perform a cutting operation. A throttle lever for adjusting an output of the engine or a rotational speed of the crankshaft is provided at the rear handle. The operator operates (pulls) the throttle lever while gripping the rear handle, and can increase a rotational speed of the crankshaft. Thus, the centrifugal clutch is connected, and the driving gear and the saw chain are driven. In this state, the cutting operation can be performed.
Generally, in a cutting machine that performs a cutting operation using a cutting tool, a state of a cutting edge changes during repeated use, and cutting performance thereof decreases. In order to restore the cutting performance, generally, a dressing operation is performed for the cutting tool. This is the same as in a chain saw, and a dressing operation is performed for the saw chain. For example, as described in Patent Literature 2, the dressing operation is performed such that, while the chain saw is stopped, the operator grinds each cutting edge of the saw chain using a rod-like saw file or the like. In addition, a dressing operation can be performed by grinding cutting edges using a grinding stone. Since this operation is performed by bringing a driven saw chain into contact with a grinding stone for a dressing operation, and cutting the grinding stone in the same manner as in a general cutting operation, it can be performed much more easily than in the above case.